Project Summary As a consequence of mammography screening, the incidence of ductal carcinoma in situ (DCIS) has increased dramatically. Over diagnosis and overtreatment are of particular concern for DCIS because the standard of care is to treat. Thus, even though their lesions are unlikely to become cancerous, a high proportion of women with DCIS undergo aggressive treatment (either mastectomy or breast conserving surgery (lumpectomy) followed by a course of radiation therapy with or without hormone therapy). Aggressive treatment of DCIS can have short and long-term deleterious health consequences (Allegra et al. 2010). Because the 10-year survival rate for women with DCIS is 96 to 99% (Allegra et al. 2010; Narod et al. 2015), many cancer specialists have raised concerns that aggressive treatment is not warranted (Esserman and Alvarado 2014). For this reason, some cancer specialists have recommended the adoption of new terminology for indolent and precancerous disorders that excludes the word carcinoma (Esserman et al. 2014). Empirical evidence documenting whether less aggressive treatment of DCIS results in adverse clinical outcomes and/or lower medical expenditures is nonexistent. Moreover, to our knowledge, no published research has considered whether provider characteristics influence aggressive treatment of DCIS. Our proposed research project addresses these significant gaps in knowledge. Our aims are: Aim 1: To evaluate if provider attributes affect receipt of aggressive treatment by women aged 65 and older with newly diagnosed DCIS, after controlling for clinical factors and patient sociodemographic characteristics. Aim 2: After controlling for potential non-random selection associated with receipt of aggressive treatment, to evaluate if women aged 65 and older with newly diagnosed DCIS who undergo more aggressive treatment have a lower probability of developing subsequent invasive breast cancer and lower mortality. Aim 3: After controlling for potential non-random selection associated with receipt of aggressive treatment, to evaluate if women aged 65 and older with newly diagnosed DCIS who undergo more aggressive treatment incur higher DCIS-related episode expenditures. Aim 4: To evaluate whether receipt of hormone therapy (tamoxifen or aromatase inhibitors) as another dimension of aggressive treatment alters the effect of receipt of aggressive treatment on the likelihood of developing subsequent invasive breast cancer, survival and DCIS-related medical expenditures. To address these aims we will merge cancer registry records for women newly diagnosed with DCIS with Medicare claims for the time period 2000-2014 to identify the types of treatments received and medical expenditures for the women following initial diagnosis. Our health outcomes, whether women with DCIS subsequently develop invasive breast cancer or die, will be derived from state cancer registry records.